Wounds occur when the integrity of tissue is compromised, affecting one or more layers of the epidermis or underlying tissue. Acute wounds may be caused by an initiating event, such as a accident-related injury, surgical procedure or by operation of an infectious disease, and generally take the form of punctures, abrasions, cuts, lacerations, or burns. Chronic wounds are wounds that generally do not heal within three months, due to one or more of: ischemia of the vessels supplying the tissue, venous hypertension or compromise of the immune response, such as observed, for example, with venous ulcers, diabetic ulcers and pressure ulcers. Depending on etiology, such as diabetes, venous insufficiency, or cardiovascular failures, acute wounds may become recalcitrant and even chronic.
The introduction of bacteria from external sources into the wound typically causes inflammation that activates the patient's immune response, in turn causing white blood cells, including neutrophil granulocytes, to migrate towards the source of inflammation. While they fight pathogens, such neutrophils also release inflammatory cytokines and enzymes that damage cells. In particular, the neutrophils produce an enzyme called myeloperoxidase that in turn is metabolized to produce reactive oxygen species that kill bacteria. Collaterally, such enzymes and reactive oxygen species damage cells in the margin surrounding the wound, referred to as the “periwound,” thereby preventing cell proliferation and wound closure by damaging DNA, lipids, proteins, the extracellular matrix and cytokines that facilitate healing. Because neutrophils remain in chronic wounds for longer than in acute wounds, they contribute to higher levels of inflammation. Moreover, the persisting inflammatory phase in chronic wounds contributes to exudate (fluid that flows from the wound) with high concentrations of matrix metalloproteases (MMPs). Excess MMPs results in degradation of extracellular matrix protein. In addition to damaging the wound, exudate damages the periwound tissue exposed to it as well. In particular, exudate that flows out of the wound and onto periwound region may damage the fragile skin, which is already compromised due to the patients underlying etiology, such as diabetes. Such damage may degrade the periwound skin and cause its breakdown and turn it into a wound. Thus, exudate flow onto the periwound region will cause many complications, including, the potential for increasing the size of the wound and prolonging its healing. Such damage to the skin in the periwound region (periwound skin) makes it more susceptible to tearing and resultant intense pain as dressings or devices adhered to them are removed. Other complications include infection of the periwound region and intense itching.
Patients suffering from chronic wounds frequently report experiencing severe and persistent pain associated with such wounds, which may arise from necrosis of and/or nerve damage of the skin and underlying tissue. Treatment for such pain often consists of low dose analgesics, while topical antibiotics and/or debridement, which seeks to remove necrotic tissue from the wound, may be used to control the bacterial load at the wound site.
Conventional wound treatment also typically involves covering the wound with a dressing to prevent further contamination and infection, to retain moisture, and to absorb exudate. While exudate contains biochemical compounds that benefit wound healing as noted above, its excessive amount in wound or its presence in the periwound region facilitates degradation of tissue, and the exudate additionally serves as a growth medium for bacteria. The consistency of exudate varies, depending on the type of wound and the stage of healing. For example, exudate may be watery, extremely viscous, or somewhere in between. Moreover, the sizes of wounds can vary greatly, as can their care.
Although a wide variety of dressings have been developed, few previously-known wound treatment systems properly manage exudate, e.g., removing a sufficient amount of exudate from the wound site, while protecting the periwound region from damaging contact with the exudate. Moreover, conventional systems typically do not address the pain created by the wound treatment system, particularly where the wound treatment system continuously contacts the wound. For example, gauze, which is applied directly onto a wound, is capable of absorbing only a limited amount of exudate, and readily transports excess exudate onto the periwound region, causing maceration and damage. Moreover, the gauze typically is in direct contact with the wound and adheres to it, so that normal motion of the patient results in rubbing, itching and discomfort. In addition, removal of the gauze at periodic intervals is painful and frequently disrupts any healing that may have occurred.
Some previously-known approaches to wound treatment attempt to reduce adhesion between the wound and the dressing by applying additional substances. For example, the wound and dressing may be soaked in saline water to loosen adherence and/or soften any scabs that formed, thus facilitating removal of the dressing. Or, for example, antibiotic ointments such as polymyxin B sulfate or bacitracin can be applied to reduce sticking. However, such methods are not always satisfactory because soaking a particular wound in water or applying ointments may not be practicable or recommended.
Some previously-known dressings are promoted as being “non-stick” or “non-adherent,” such as TELFA™ and XEROFORM™, and other brands that may be composed of materials such as hydrocolloids, alginates, and hydrofilms. Regardless of the level of adherence of such dressings to the wound, continuous contact between the dressing and wound disturbs the fragile wound matrix, and may undermine the growth of blood vessels and epithelial cells in the wound bed. Such disturbance often occurs when the dressing is removed, or simply as a result of the contact between the bandaged area and the patient's environment. Pain is often concomitant with such disturbances. In addition, previously-known “non-stick” dressings usually do not absorb sufficient amounts of exudate, and thus require frequent monitoring and changing. These drawbacks add to the cost of use and limit the applicability of such previously-known wound treatment systems.
Previously-known dressings commonly have only a limited ability to manage wound exudate. As noted above, prolonged exposure of otherwise healthy skin to exudate may cause degradation of the periwound region. The moisture of the exudate may cause maceration, which is a softening of the skin that compromises its integrity and makes the skin in the periwound region vulnerable to physical insult and infection.
Some previously-known dressings attempt to manage exudate to address the foregoing issues, but provide either limited benefit and/or at a much higher perceived cost. For example, a foam dressing such as ALLEVYN® (marketed by Smith & Nephew, Largo, Fla., USA) is designed to absorb large amounts of exudate. However, use of this product is restricted to highly exuding wounds, because its highly absorptive properties can result in desiccation of wounds that are not highly exuding, thereby impeding healing. In addition, because foam used in that product cannot be conformed to the size and shape of the wound, the dressing typically overlaps with the periwound region. Consequently, exudate absorbed by the foam is transported throughout the foam and onto the periwound region, where prolonged exposure leads to maceration and degradation of the periwound region. Other previously-known dressings, such as ACQUACEL® hydrofiber dressing (available from ConvaTec, Inc., Princeton, N.J., USA) contact the wound bed, and are intended to absorb exudate and transfer and sequester the exudate in a layer disposed atop the wound. This and similar previously-known dressings do not entirely contain or absorb exudate. Moreover, like foam and other previously-known dressings, hydrofiber dressings essentially plug the wound surface, and create an osmotic environment in which the fluidic osmotic pressure within the wound bed approximates that of the surrounding tissue. Consequently, exudate is not sufficiently drawn from the wound, and its buildup in the wound may adversely affect the wound and periwound region. Furthermore, ALLEVYN®, ACQUACEL®, and similar previously-known dressings do not provide an adequate moisture vapor transfer rate (MVTR) away from the wound environment, thus creating the potential for an over-hydrated environment that hinders wound healing.
Other previously-known wound treatment systems, such as the V.A.C.® system, available from Kinetic Concepts, Inc. (San Antonio, Tex., USA), employ a mechanically operated contact-based dressing that continuously vacuums exudate from the wound bed. It and other dressings incorporating the concept of Negative Pressure Wound Therapy have proven particularly useful in healing large wounds, such as surgical wounds. However, such systems are costly, difficult to apply and time consuming. In addition, because such systems require insertion of a sponge (for the V.A.C.® system) or gauze (as commercialized by other wound care companies) directly into the wound bed, they likely cause considerable pain and discomfort for the patient, and may not be appropriate for many types of wounds.
Several previously-known dressings also have been developed that are promoted as “non-contact” dressings, which seek to prevent adhesion of the wound tissue to dressing, or to facilitate certain treatments that by their nature cannot contact the wound, e.g., thermal therapy. Such dressings are commonly formed as an inverted cup or a raised bandage that covers the wound without contacting it. Such previously-known dressings, however, also have failed to adequately heal wounds and protect the periwound region. Such non-contact dressings are provided in pre-formed shapes and sizes, and have limited deformability, thus limiting their ability to prevent exposure of the periwound skin to exudate. Additionally, the limited deformability of such previously-known dressings makes application of such dressings difficult or impossible to wounds on small surfaces or in areas with complex topology, such as the ankle or foot. Previously-known non-contact dressings also do not allow the pressure applied to the periwound region to be readily managed, and may result in the formation of pressure rings around the wound, thereby inducing ischemia in the wound and surrounding tissue. Finally, such previously-known dressings do not provide any mechanism to stimulate the flow of exudate, nor do they sequester exudate away from the wound in any appreciable volume. Such previously-known dressings also trap humidity over the wound and periwound region, leading to maceration, periwound degradation and impeded healing.